<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        input {
            color: #999;
        }
        
        .inputfocus {
            border: 1px solid pink;
            outline: none;
            color: #333;
        }
    </style>

</head>

<body>
    <input type="text" value="手机/邮箱">
    <script>
        var input = document.querySelector('input');
        input.onfocus = function() {
            if (input.value == '手机/邮箱') {
                input.value = '';
                // input.style.border = '1px solid pink';
                // input.style.outline = 'none';
                // input.style.color = '#333';
                input.className = 'inputfocus';
            }
        }
        input.onblur = function() {
            if (input.value == '') {
                input.value = '手机/邮箱';
                input.style.color = '#999';
            }
        }
    </script>

</body>

</html>